Piston and like packing device



c. A. osLlNG 2,340,466

PISTON ND LIKE PACKING DEVICES Filed Aug. 2o, 1940 CLVE A USTN GOS L/Nq/Nvf/VTQ? ATTOI? EY Patented Feb. l,

erica PISTON AND LIKE PACKING DEVICE Clive Austin Gosling, London,England, assigner to Automotive Products Company Limited,

London, England Application August 20, 1940, Serial No. 353,409 In GreatBritain September 1, 1939 4 Claims.

This 'invention relates to piston and like packing devices, and it hasfor its primary object to provide an exceptionally simple form of sealwhich is capable of resisting leakage of Iiuid in either direction. Theinvention is intendedmore particularly for the packing ring which isemployed at the tail end of the piston of hydraulic master cylinderunits where the piston is reduced in diameter intermediate its length soas to form an annular chamber connected with the usual reservoir of thesystem.

According to the present invention, a piston or like packing devicecomprises a single ring formed from rubber or like mouldable elasticmaterial, and provided with a pair of lips which,

when the packing device is in position, are directed axially ,inopposite directions to prevent leakage of fluid across the packing fromeither side.

The packing may comprise a ring of substantially U-shaped cross-section,one limb of which forms the main body` of the packing, whilst Vtheother'limb forms one lip.

According to a further feature of the invention, there is provided in amaster cylinder unit of a hydraulic braking system, a piston packingcomprising a ring which is moulded from rubber or equivalent elasticmaterial and is formed with two lips which, when the packing is inposition are directed, one forwardly ,to prevent leakage of liquid fromthe reservoir, and one rearwardly to prevent air from being drawn intothe system during the retracting movement of the piston.v

The rearwardly directed lip of the packing may be of generally roundedsection; the forwardly directed lip may project obliquely outwardly fromthe substantially rectangular ring forming the main body of the packing,and be undercut at its junction therewith, the rearwardly directed lipcomprising a substantially rounded rib formed' on the outer rear cornerof the rectangular ring by cicumferential grooving of'the outer and rearVto which the invention is applied;

Figure 2 is a cross section of one form of piston packing according tothe invention;

Figure 3 is a fragmentary view of a master cylinder piston With apacking according to the invention in position thereon; and

Figures 4 and 5 are views corresponding to Fig-- ures 2 and 3, butshowing a modied form of the invention.

Referring to Figure 1, the braking system comprises a master cylinderIll having a reservoir il cast integral therewith, a piston l2 beingmovable forwardly in the cylinder by means of a pedal i3, and beingreturned by a spring l. 0n the piston head l5 is a cup packing l5 makinga uuid-tight joint with the cylinder so that as the piston is movedforward by the pedal, liquid pressure is created in the cylinder. Thepiston l2 is reduced in diameter behind its head to form an annularchamber il connected by a port lli with the reservoir ll, so that thechamber il is constantlir filled with liquid. A second port l0 of smalldiameter connects the reservoir and the cylinder, being just forward ofthe cup packing it when the piston is fully retracted. The cylinder l0is connected by piping 2l to motor cylinders 22 (only one of which isshown) acting to spread apart brake shoes 23, 2li acting on drums ineach of the four wheels 25 ofthe vehicle to which the braking system isiitted.

Forward movement of the piston l2 due to pressure on the pedal i3 causesthe cup packing vlli to pass over the port i9, and then to'force liquidfrom the master cylinder through the pipelines 2i to the motor cylinders22, thus applying the brake shoes to the drums, and the pressure exertedon the pedal is transmitted through the liquid to the shoes. When thepedal is released, the piston l2 is returned by the spring lil towardsits retracted position, thus allowing the liquid previously forced intothe pipelines 2l to return into the master cylinder under the pressureexerted on the motor .cylinder pistons by the brake shoe pull-olfsprings. Owing to the restricted cross-section of the pipe-lines, thepiston i2 may return so rapidly that liquid from the pipelines does notreturn to the cylinder quickly enough to follow up its movement andmaintain the cylinder full. In that event the cup I6 collapses andpermits liquid from the chamber il to enter the cylinder through ports2U in the piston head, thus keeping the cylinder full of liquid. Surplusliquid ithus drawn into the cylinder returns to the reservoir ll throughthe port i9, when the piston reaches its retracted position, beingvdis-- placed by that returning from the pipelines..

To retain liquid in the chamber l1, and to prevent the entry of airthereinto, a packing 20 is provided at the rear or tail end of thepiston. The piston I2 has at its extreme rear end a ilange 2l which is aworking tin the cylinder lll, and spaced from this flange so as to forman annular groove is a circumferential ri-b 28 of somewhat less diameterthan the flange. The packing 26, which is shown on a larger scale inFigure 2 and 3 is substantially U-shaped in cross-secti n, one limb 23of the U forming the main body of the packing, and being accommodatedbetween the flange 21 and rib 28 on the piston, whilst the other limb isformed by an undercut lip 3| facing towards the head of the piston, andserving to prevent the passage of liquid outwardly towards the rear endof the cylinder. A second lip 32 is formed on the outer rear corner ofthe body 29 of the packing, by grooving the outer and rear surfaces ofthe ring at 33 and 34 respectively, the lip 32 being of rounded shape.Figure 2 shows the packing 26 in its initial form before mounting on thepiston, and it will be seen that the lip 32 projects outwardly at anangle of about 45 to the axis of the packing, whilst the lip 3|, whichis of trapezoidal form projectssubstantially axially, but has its innerand outer surfaces lying at an angle of about 20 to the axis. In Figureu"3 the packing 26 is shown mounted on the piston.

and inserted in the cylinder l0. The main body 29 of the packing iitsclosely between the a'nge 21 and the rib 28, the base of the groovebetween these parts being slightly greater in diameter than the interiorof the part 29 of the packing, so that the latter engages rmly with thebase of the groove and tends to expand axially to engage firmly both thewalls of the groove. The insertion of the piston in the cylinderdistorts both lips somewhat inwardly, the lip 3| tending to bend aboutits junction with the main body 29 of the packing, so that the outerinclined surface of the lip approaches an axial position and lies alongthe wall of the cylinder, whilst the radially inner part of the lip isturned inwardly and rearwardly to bear on the forward face of the rib23.

` The lip 3| thus presents to the chamber I1 an inclined surface slopingrearwardly from the cyl,- inder wall to provide an acute angle at itsjunctionwith the outer face of the packing, and liquid pressure in thecylinder acts on this sloping surface to urge the packing against thecylinder wall. The undercutting of the llip 3| is deep enough' toprovide a clearance space 35 around the periphery of the rib 28, andthere is also clearance between the inner wall of the lip 3| and theadjacent wall of the piston. It will be seen that,

owing to their distortion on assembly, both lips 3| and 32 engage thecylinder wall with some degree of initial interference, and thus areable to prevent leakage when the pressures acting are very low.

Figures 4 and 5 show a form of packing slightly different from thatshown in Figures 2 and 3,-

though having the same general characteristics. The lip 3| is formedwith an additional relatively small axially directed lip 36 providing athin forward edge to the main lip, and the forward face of the lip 32 issubstantially perpendicular to the I axis of the packing, thus providinga greater area of that lip to contact with the cylinder wall. Theperipheral surface of the lip 3| is formed. to

a conicity of less angle than in the form of pack- It is Well-known thata packing ring of the type described in this specification, when movingrelatively to the cylinder barrel is subject to considerable frictionalresistance, and that, generally speaking, the more effective the sealprovided, the greater the friction, particularly when the pack'- ing ismoving towards the direction from which the pressure to be sealed isacting. In a hydraulic master cylinder unit, the piston is usuallyreturned by a spring such as the spring I4 in Figure 1, and in orderthat the piston may return suiiiciently quickly after an application ofthe brakes to be ready for a second application in a `short tima-thefrictional resistance to the return movement of the piston must be keptlow.I For this reason, it has not been customary to 'provide arearwardly projecting lip on the packings hitherto used in the place ofthe packing 26, Figure 1, the small pressure difference across thepacking being relied upon to prevent the entry of airA into thecylinder. It has been found, however, that such packings are notentirely satisfactory, as air tends to leak to some extent into thecylinder, and the' packing of the present invention has been designedwith the object of providing a rearwardly facing lip which, whilstpresenting a sufficient degree of resistance to the entry of air, doesnot increase the frictional resistance to movement of the pistonsufficiently to affect seriously7 the time required by the piston toreturn to its retracted position under the iniiuence of its returnspring.

What I claim is:

1. For use with a piston and cylinder unit, a packing device mounted onand moving with the piston comprising a single ring of substantiallyU-shaped cross-section formed from moldable elastic material andprovided with a pair of lips I of the aforesaid lips, and the second lipcomprising an inclined circumferential rib onvthe main body of thepacking.

2. The combination of a piston having a circumferential groove thereinone side of which'is formed by a circumferential rib projecting from thepiston, with a packing device mounted on and moving with the `pistoncomprising a single ring of substantially U-shaped cross-section formedfrom moldable elastic material and provided with a pair of lips whichcontact the cylinder wall and which are directed axially in oppositedirections to prevent leakage of iiuid across the packing from eitherside, one limb of the U constituting the main body of the packing andextending into the circumferential groove on the piston while the otherlimb forms one of the aforesaid lips, and the second lip comprising aninclined circumferential rib on the main body of the packing.

3. In a master cylinder unit of a hydraulic braking system, a pistonpacking comprising a ring which is molded from rubber or equivalentelastic material, said packing ring having a substantially rectangularcross-section portion iorm. ing the main body thereof and having twolips e which, when the packing is in position, are directed. oneforwardly to prevent'leakage of liquid from the reservoir, and onerearwardly to prevent air from being drawn into the system during theretracting movement of the piston, said forwardly directed lipprojecting obliquely outwardly 'from the substantially rectangularcross-section portion which forms the main body of the packing ring andbeing undercut at its junction therewith, said rearwardly directed lipcomprising a substan. tially rounded rib fonned on the outer rear cornerof the substantially rectangular cross-section portion bycircumferential grooving of the outer and rear faces of the ring.

4. In a master cylinder unit of a hydraulic braking system, a pistonpacking comprising a ring which is molded from rubber or equivalent eelastic material, said packing ring having a substantially rectangularcross-section portion forming the main body thereofand having two lipswhich, when the packing is in position, are directed, one forwardly toprevent leakage of liquid from the reservoir. and one rearwardly toprevent air from being drawn into the system during the retractingmovement of the piston, said Iorwardly directed lip being ofsubstantially trapezoidal shape in cross-section and projectingobliquely outwardly from the substantially rectangular cross-sectionportion which forms the main body of the packing ring, and beingundercut at its junction therewith, said rearwardly directed lipcomprising a substantially rounded rib formed on the outer rear cornerof the substantially rectangular 'cross-section portion bycircumferential grooving of the outer and rear faces of the ring. v

OLIVE AUSTIN GOSLING.

